In a string instrument the vibrations in the sound body are transmitted to the bridge supported thereon and therethrough to the end piece or connection part of each of the strings which extend between the bridge and the string holder or tailpiece of the instrument. Thus the vibrations of each of the strings are transmitted to the sound body of the instrument and then back through the bridge to the end pieces of the strings. For this reason a phase shift can exist between the sympathetic vibration of the end pieces of the strings and the vibration in the sound body, depending on the reaction frequency to which each of these string end pieces is tuned. This so-called reaction frequency is determined by the diameter, tension, and length of the string end piece.
The result is occasionally disturbing vibrations which combine with the desired vibrations or subtract from them to produce a sound which is occasionally far from the desired sound.
When this effect is excessively dominant a good musician will frequently tip or displace the bridge, or shorten the tail piece. It is also kown to mute the end pieces of the strings or otherwise damp vibrations thereof.